What is a normal year? Many of the recommendations and much of the advice pertaining to farming is based on what happens in a normal year. Take for incidence internal parasite control in lambs. The general recommendation for the normal year is to dose mid-season lambs at 5-6 weeks of age, at 10 weeks, at weaning and every 4-8 weeks thereafter depending on system, pasture management, product used etc.

In my own situation, with ewes starting to lamb on March 14, that translates into dosing lambs during the first week in May, the first week of June and the first week of July when lambs are weaned. Over the past few years I have had a niggly problem with a few lambs dying at around eight weeks old. Lambs are dull, develop a scour, appear thirsty (heads in water trough), develop a peculiar gait and rapidly become emaciated. Despite various treatments, they invariably died.

Two lambs were sent to the Regional Veterinary Laboratory in Kilkenny last year where nephrosis (kidney disease) was diagnosed. The cause of this disease is not really understood but there are suggestions that it may be related to nematodirus infection. Nematodirus is the first worm species to infect lambs and generally occurs during April and May.

In order to shed some light on the problem, worm egg counts were carried out on faecal samples from single and twin lambs, starting in early May, and the results were quite interesting. There was only around 100 nematodirus eggs per gram up to May 9. By May 12, the count had reached 465 eggs per gram and the lambs were dosed on May 14. I noticed a few lambs scouring on June 6 and immediately carried out a count that showed more than 1,000 eggs per gram. Lambs were dosed the next day.

The points I would make regarding this exercise are:

If I had dosed the lambs as normal it would have been a total waste of time and money.

The wormer only eliminates the adults that are present at the time of dosing.

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As none of the worm doses on the market possess any residual activity against nematodirus, dosing in early May of this year was still likely to result in high counts by mid-May.

I was surprised at the rapid build up of eggs from when the lambs were first dosed between May 14 and June 6 -- just 23 days. If the dosing didn't start on May 14, this count would most likely have been much higher. It is almost certain that I would have lost lambs. I should have dosed earlier than June 6, but I was caught off guard. One could argue that, while the earlier-born lambs have developed some immunity, the later-born lambs have suffered damage.

As it will take a year for the majority of the nematodirus eggs to develop and hatch, the pastures grazed up to June are likely to be sources of infection for next year's lamb crop.

The faecal egg counts from triplet lambs that were grazed separately were relatively low up to mid-May. These lambs were on meals and, as a result, were taking in less grass and, hence, less parasites.

This year, the nematodirus hatch occurred late, at a time when susceptible lambs were taking in substantial amounts of grass, resulting in the problems experienced by flock owners.

The fact that there was little grass, and lambs were grazing at a much lower level, exacerbated the condition.

There was no case of nephrosis this year but it will take another few years of faecal sampling to confirm that proper nematodirus control eliminates the condition.